1. Field of the Invention
The present invention relates to a heat exchanger made of aluminum (the term "aluminum" in the specification and claims of this application refers to metal aluminum as well as an aluminum alloy) and a method of manufacturing such a heat exchanger. A heat exchanger made of aluminum is suitable for an evaporator in a refrigerant circuit, such as an evaporator for an air conditioner of an automobile.
2. Description of the Related Art
Conventionally, an evaporator is designed to have a cooling part having as large an area as possible, to enhance the cooling effect and to make the gaps between fins as small as possible, and thus reduce the size of the evaporator. Accordingly, moisture in the air condenses in the gaps between the fins and the condensed water droplets cause a white rust corrosion. Further, since the atmosphere in the gaps between the fins is very humid, due to the condensed water, and the evaporator usually has a complex shape, dust in the air is easily deposited and accumulated on the fins. Accordingly, fungi are grown in the fin gaps and an unpleasant odor is given off by the fungi.
To solve these problems, the heat exchanger proposed in Japanese Unexamined Patent Publication (Kokai) No. 61-250495 (the application of which is the priority basis for Ohara et al. U.S. Pat. No. 4,830,101 is manufactured by a chemical conversion treatment of a surface of an aluminum-based metal body with a chromate, or a phosphate, etc. to impart a corrosion resistant coating on the metal body and then coating a resin layer on the chemical conversion coating to impart an hydrophilic property (wettability) thereto. The resin coating is a polymer having, many amino groups in the molecule. This prevents a corrosion caused by a deposition of condensed water on a surface of an aluminum body, and a growth of fungi due to the deposited water.
Optionally, an antifungal agent is added to the resin coating to inhibit a growth of fungi, or a deodorizer agent is added, to ensure the comfort of the user.
Nevertheless, it was found that the above resin coating containing a polymer having many amino groups in the molecule is not durable and cannot be used for a long time. The inventors carried out various experiments, and found from the results that the resin coating is only weakly bound to the chemical conversion coating. Accordingly, the resin coating is peeled off with a lapse of several years of use, and is dispersed as a fine powder. This fine powder irritates the olfactory organ of a user and produces an undesirable feeling of discomfort. The unpleasant odor is caused by not only the above fine powders but also fungi, and although an antifungal agent or a deodorizer is conventionally added to the resin coating to prevent a growth of fungi or an unpleasant odor, the antifungal agent or the deodorizer is also dispersed, together with the resin coating, in the air and thus are not adequate in practice.
The inventors first found that the unpleasant odor is caused not only by a growth of fungi but also by a remarkable growth of bacteria and yeast. Namely, it was not known that the main cause of the odor, other than the fine powder, is the fungi, and it also was not known that an unpleasant odor is formed by oxidation decomposition reactions of the bacteria and yeast. Hereinafter, fungus, bacteria and yeast are collectively referred to as a microorganism.
In this connection, 2,2'-dithiobis(pyridine-1-oxide) is known to have an antimicrobial effect, and therefore, is used in shampoos and soaps, etc.
The object of the present invention, in consideration of the above problems, is to provide an aluminum heat exchanger having a long lasting corrosion resistance, and on which a growth of microorganisms is inhibited for a long period, and to provide a method of manufacturing same.